1. Field of the Invention
The present invention relates to apparatus for electrically interconnecting parts on the steering wheel and column, respectively, of a motor vehicle.
2. Description of the Prior Art
In recent years, as automobiles have been electronically controlled, electronic control switches have been fitted on the steering wheels of steering device of automobiles. It is necessary to electrically wire the switches to parts on the steering columns. The steering wheels can rotate more than 360.degree. in both directions. In order to electrically interconnect parts on the steering wheel shaft and the steering column of an automobile, there is a need of an apparatus including a rotating body fixed to the shaft, a fixed body fixed to the column, and a flexible flat cable (which will be referred hereinafter to as an FFC), which generally has plural lead wires, housed between the bodies. The FFC may be either vortically wound or vortical and turned back midway.
In general, such an apparatus includes a first rotator and a second rotator, as rotating cylindrical bodies, which surround and are fixed to the steering wheel shaft of an automobile, and an upper cover and an under cover, as fixed cylindrical bodies, which rotatably support the peripheries of the rotating bodies and are fixed to the steering column. An annular space is formed between the rotating bodies and the fixed bodies. Housed in the space is a FFC for electrically interconnecting parts on the steering wheel and column.
In general, the under cover has an upward opening cylindrical wall. Fitted inside the cylindrical wall is an internal gear slightly smaller in diameter than the inner diameter of the wall. The internal gear has ribs projecting from its outer periphery for positioning it and preventing it from rotating. The ribs are spaced at different angles circumferentially of the internal gear. The under cover has inner recesses in its cylindrical wall. Each of the ribs engages with one of the recesses.
Because the ribs are spaced circumferentially at different angles, the internal gear can be positioned uniquely in place and prevented from rotating relatively to the under cover.
In fitting the internal gear inside the cylindrical wall of the under cover, however, the internal gear is positioned relatively to the cover by engaging the ribs, which are spaced at different angles, with the recesses, so that it is difficult to determine the position and wrong positioning may occur. As a result, there is a need of a process for inspecting the positioning of the internal gear, or a process for correcting its position, so that the production costs are high.
In addition, the ribs engage with or lap over the recesses in a small amount. Therefore, when the FFC has reached its critical position of rotation, i.e., if the first rotator is rotated further after the FFC is all wound on the rotator, the FFC is pulled, so that torque is exerted on the internal gear. As a result, the ribs may disengage from the recesses, so that the internal gear rotates relatively to the under cover. Thus, the strength of the ribs and recesses is not enough to position or fix the internal gear relatively to the under cover.